Wafer polishing method

ABSTRACT

A wafer polishing method is provided. First, a wafer, having a first surface, a second surface, and a plurality of opening portions depressed on the first surface, is provided. A plastic adhesive is filled in the opening portions and cured later. A polishing step is performed to thin the thickness of the wafer. Therefore, the yield of the wafer in the polishing process can be improved by the protection of the plastic adhesive.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 96142073, filed on Nov. 7, 2007. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a wafer polishing method, inparticular, to a wafer polishing method capable of preventing wafercracks.

2. Description of Related Art

Microelectromechanical system (MEMS) is a microelectromechanicalcomponent fabricated in a microminiaturized package structure, and thefabricating technique thereof is quite similar to the technique offabricating integrated circuits (ICs). However, interactions, forexample, about mechanics, optics, or magnetic force between the MEMSdevice and surrounding environment are more than that of theconventional IC.

The MEMS device may include micro-sized electromechanical components(for example, switches, mirrors, capacitors, accelerometers, sensors,capacitive sensors, or actuators etc.), and the MEMS device may beintegrated with the IC in a manner of single block, thereby greatlymodifying insertion loss or electrical isolation effect of the overallsolid-state device. However, in the macroscopic world of the entirepackage structure, the MEMS device is extremely weak and may be impactedby slight static electricity or surface tension at any moment to causefailure. Therefore, in order to prevent the MEMS device fromcontaminations or damages, usually the MEMS device is sealed in a cavityof the wafer.

FIG. 1 is a schematic view of cracks generated in a conventional waferpolishing process. Referring to FIG. 1A, the wafer 100 has a pluralityof lattice opening portions 102 (or cavities). However, in the polishingprocess, since the strength at regions A and B becomes weak, the regionsA and B (for example, the edges) of the wafer are usually cracked, andsilicon residue 104 easily clogs the opening portions 102. Therefore,the present invention is mainly directed to overcome serious defectssuch as cracks and residues occurred in the polishing process.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a wafer polishingmethod, which is contributive to overcome the conventional defects andimproving the yield in the polishing process.

The present invention provides a wafer polishing method, which includesthe following steps. A wafer, having a first surface, a second surface,and a plurality of opening portions depressed on the first surface, isprovided, and the wafer has a thickness. A plastic adhesive is filled inthe opening portions and cured later. A polishing step is performed forthe wafer.

In an embodiment of the present invention, the opening portions areformed by dry etching, and depths of the opening portions are smallerthan the thickness of the wafer. In another embodiment, the openingportions are formed by wet etching, and depths of the opening portionsare smaller than or equal to the thickness of the wafer.

In an embodiment of the present invention, the process of filling aplastic adhesive in the opening portions includes adhesive dispensing orspin coating. A material of the plastic adhesive includes a liquidadhesive. In addition, the process of curing the plastic adhesiveincludes ultraviolet (UV)-thermal curing.

In an embodiment of the present invention, the process of performing apolishing step includes the following steps. A first adhesive tape isadhered to the first surface of the wafer. The second surface of thewafer is Polished until the opening portions and the plastic adhesiveare exposed. The first adhesive tape and the plastic adhesive areremoved.

In an embodiment of the present invention, before removing the firstadhesive tape and the plastic adhesive, the method further includesinverting the wafer to make the first surface of the wafer face upward.Next, a second adhesive tape is adhered to the second surface of thewafer. Then, the plastic adhesive is heated, such that the plasticadhesive is heated to separate from the opening portions.

The present invention adopts the plastic adhesive, so as to provide anappropriate protection for the wafer in the polishing process, andrelatively improve the yield of the wafer, and further the wafer afterthe polishing process has nondefective lattice opening portions.

In order to have a further understanding of the features and theadvantages of the present invention, a detailed description is given asfollows with the embodiment and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic view of cracks generated in a conventional waferpolishing process.

FIGS. 2A to 2F are schematic views of a wafer polishing method accordingto an embodiment of the present invention.

FIGS. 3A to 3C are schematic views of the wafer polishing methodaccording to another embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

FIGS. 2A to 2F are schematic views of a wafer polishing method accordingto an embodiment of the present invention. The method includes thefollowing steps.

First, in a first step, the wafer 200, having a first surface 202, asecond surface 204, and a plurality of opening portions 206 depressed onthe first surface 202, is provided. The wafer 200 has a thickness d.

Referring to FIG. 2A, in the first step of this embodiment, a dryetching or a wet etching is performed on the first surface 202 of thewafer 200, so as to form a plurality of opening portions 206 (orcavities) on the first surface 202 of the wafer 200, and depths of theopening portions 206 are smaller than the thickness d of the wafer 200.

Next, in a second step, a plastic adhesive 210 is filled in the openingportions 206 and cured later. The plastic adhesive 210 is, for example,a liquid adhesive that is thermal curable.

Referring to FIG. 2B, in the second step of this embodiment, the methodof filling the plastic adhesive 210 in the opening portions 206 includesfilling each opening portion 206 by the adhesive dispensing or spincoating process. The plastic adhesive 210 is cured through a crosslinkreaction generated when heated or heated by UV light. The cured plasticadhesive 210 functions as a protection colloid covered on the wafer 200and fills each opening portion 206. Thus, the strength of the wafer 200will not become weak when the opening portions 206 are etched, therebyproviding protection to the wafer 200.

Next, in a third step, a polishing step is performed, so as to thin thethickness d of the wafer 200. The polishing step includes the followingprocesses. A first adhesive tape 220 is adhered to the first surface 202of the wafer 200, and the second surface 204 of the wafer 200 is made toface upward. An overall polishing is performed on the second surface 204of the wafer 200 with a polishing pad until the opening portions 206 andthe plastic adhesive 210 are exposed. The first adhesive tape 220 andthe plastic adhesive 210 are removed.

Referring to FIGS. 2C to 2D, in the third step of this embodiment, whenthe first adhesive tape 220 is adhered to the first surface 202 of thewafer 200, and the second surface 204 of the wafer 200 is made to faceupward, the overall polishing is performed on the second surface 204with a polishing pad of a chemical-mechanical polishing machine (notshown), so as to thin the thickness d of the wafer 200. At this time,the plastic adhesive 210 is filled in the opening portions 206 of thewafer 200, such that the silicon residue taken away by the polishing padmay leave the second surface 204 of the wafer 200 through a cleaningsolution instead of clogging the opening portions 206. In addition, theplastic adhesive 210 provides the appropriate protection to the wafer200 in the polishing process, such that the wafer 200 is not liable togenerate cracks and other serious defects, thereby improving the yield.

In FIGS. 2E to 2F, before removing the first adhesive tape 220 and theplastic adhesive 210, the wafer 200 is first inverted, such that thefirst surface 202 of the wafer 200 and the first adhesive tape 220 faceupward. Next, a second adhesive tape 230 is adhered to the secondsurface 204 of the wafer 200. Finally, the first adhesive tape 220 andthe plastic adhesive 210 are removed. It should be noted that the firstadhesive tape 220 and the plastic adhesive 210 may be removed by heatingthe plastic adhesive 210. At this time, the adhesion strength of theplastic adhesive 210 becomes weak, and the plastic adhesive 210 shrinksunder heating so as to easily separate from the opening portions 206.Therefore, after tearing off the first adhesive tape 220, the plasticadhesive 210 can be easily removed.

FIGS. 3A to 3C are schematic views of the wafer polishing methodaccording to another embodiment of the present invention. When a wetetching capable of achieving a high aspect ratio is performed on a firstsurface 302 of a wafer 300 to form a plurality of opening portions(cavities) penetrating to a second surface 304, depths of the openingportions 306 are equal to the thickness d of the wafer 300. At thistime, in a first step, the wafer 300 is adhered to the first adhesivetape 310. Then, in a second step, a plastic adhesive 320 is filled inthe opening portions 306 and cured later. Next, in a third step, apolishing step is performed, so as to thin the thickness d of the wafer300. Similarly, the plastic adhesive 320 provides a protection for theopening portions 306 of the wafer 300, such that the cracks, the siliconresidue, and other serious defects will not easily occur, therebyimproving the yield. In addition, the plastic adhesive 320 may beremoved by heating that weakens the adhesion strength of the plasticadhesive 320, and the plastic adhesive 320 shrinks under heating andeasily separate from the opening portions 306. Therefore, after tearingoff the first adhesive tape 310, the plastic adhesive 320 can be easilyremoved.

In view of the above description, the present invention use the plasticadhesive to provide an appropriate protection to the wafer in thepolishing process and relatively improve the yield of the wafer, suchthat the wafer after polishing has non-defective lattice openingportions (or cavities), for performing the subsequent packagingprocesses for MEMS system, thereby sealing the MEMS device in thecavities of the wafer.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A wafer polishing method, comprising: providing a wafer comprising afirst surface, a second surface, and a plurality of opening portionsdepressed on the first surface and the wafer having a thickness; fillinga plastic adhesive in the opening portions, and curing the plasticadhesive; adhering a first adhesive tape to the first surface of thewafer; performing a polishing step to polish the second surface of thewafer until the plastic adhesive filled in the opening portions isexposed; heating the plastic adhesive to separate the plastic adhesivefrom the opening portions; and removing the first adhesive tape and theplastic adhesive at the same time by peeling off the first adhesivetape.
 2. The wafer polishing method according to claim 1, wherein theopening portions are formed by dry etching, and depths of the openingportions are smaller than the thickness of the wafer.
 3. The waferpolishing method according to claim 1, wherein the opening portions areformed by wet etching, and depths of the opening portions are smallerthan or equal to the thickness of the wafer.
 4. The wafer polishingmethod according to claim 1, wherein the process of filling a plasticadhesive in the opening portions comprises adhesive dispensing or spincoating.
 5. The wafer polishing method according to claim 1, furthercomprises adhering a second adhesive tape to the second surface of thewafer.
 6. The wafer polishing method according to claim 1, wherein amaterial of the plastic adhesive comprises a liquid adhesive.
 7. Thewafer polishing method according to claim 1, wherein the process ofcuring the plastic adhesive comprises ultraviolet (UV)-thermal curing.8. The wafer polishing method according to claim 1, wherein beforepolishing the second surface of the wafer, making the second surface ofthe wafer face upward.
 9. The wafer polishing method according to claim8, wherein before removing the first adhesive tape and the plasticadhesive, the method further comprises inverting the wafer to make thefirst surface of the wafer face upward.
 10. The wafer polishing methodaccording to claim 9, wherein after inverting the wafer, the methodfurther comprises adhering a second adhesive tape to the second surfaceof the wafer.